[x3d-public] height and slope TextureCoordinateGenerator modes

[Andreas Plesch]

Thanks, Roy, for following up and raising the issue on the Mantis tracker.

It may or may not be relevant but I think I tracked down what inspired the
TextureCoordinateGenerator modes. I think it may be the glTexGen opengl
function:

https://www.opengl.org/sdk/docs/man2/xhtml/glTexGen.xml

The opengl manual page above even mentions the example of contouring
terrain (!), and I suspect that the "VERTEX" mode is supposed to correspond
to GL_OBJECT_LINEAR function in some way but I could not find an
implementation of the VERTEX mode sofar. So perhaps a VERTEX mode with a
parameter field value of "0 1/height_range 0 0" would more or less
correspond to the proposed "HEIGHT" mode ?

I think it would make sense to have user-friendly, more targeted modes with
sensible defaults as outlined.

The glTexGen function is not available in webGL. It could be recreated in a
shader as suggested here

http://stackoverflow.com/questions/5062301/gltexgen-in-opengl-es-2-0

-Andreas


On Tue, Jul 21, 2015 at 2:26 PM, Roy Walmsley <roy.walmsley at ntlworld.com>
wrote:

> Andreas,
>
>
>
> Thank you very much for your extremely interesting and thoughtful
> suggestions below.
>
>
>
> I have raised a Mantis issue on your behalf, directly copying in all of
> your submission. It is Issue 831 (
> http://www.web3d.org/member-only/mantis/view.php?id=831) for tracking.
> Your comments will be passed to one of the working groups for consideration
> and possible inclusion in the next X3D specification release. We will keep
> you informed of further developments.
>
>
>
> Regards,
>
>
>
> Roy Walmsley
>
>
>
> *From:* x3d-public [mailto:x3d-public-bounces at web3d.org] *On Behalf Of *Andreas
> Plesch
> *Sent:* 20 July 2015 15:36
> *To:* X3D Graphics public mailing list
> *Subject:* [x3d-public] height and slope TextureCoordinateGenerator modes
>
>
>
> This is a request of feedback on potential new height and slope modes for
> TextureCoordinateGenerator and their suitability for inclusion in new
> versions of the X3D specification.
>
>
> The TextureCoordinateGenerator node offers a number of modes intended for
> advanced graphics effects such as (pseudo-)reflections:
>
>
>
> http://www.web3d.org/documents/specifications/19775-1/V3.3/Part01/components/texturing.html#t-Texturecoordgeneration
>
>
>
> Many modes involve the eye position which is dynamic and therefore
> requires dynamic generation of texture coordinates. The other intention of
> the node seems to be more of a helper node to enable easy generation of
> static texture coordinates. SPHERE-LOCAL, VERTEX and NOISE modes fall into
> this category as I understand them.
>
> Is this a fair description of the purpose of the
> TextureCoordinateGenerator node ? What does the VERTEX mode do ? Literally
> use the x and y (or z?)  components of a vertex as texture coordinates
> (which then could be scaled with a TextureTransform) ?
>
> In data visualization it is often useful to color the y component (height)
> of a mesh. This is particularly evident for ElevationGrids where contouring
> is a proven visualization method. Therefore it would be very useful to have
> a new HEIGHT mode which generates texture coordinates based on the y
> coordinate. The most useful default would be to automatically scale to the
> range in height of the mesh. The parameter field could be used to define a
> custom range in height which corresponds to the 0 to 1 range of the S
> texture coordinate. T would be set to 0, eg. a 1d texture map would be
> expected.
>
> Here is an example of the use a height mode:
>
>
> http://andreasplesch.github.io/x3dom/GeoElevationGrid_texture/terrain_height.xhtml
>
> which was tentatively implemented in a forked x3dom (Mesh.js).
>
> Similary, it is often useful to visualize the spatial gradient of a
> surface or the slope. A new SLOPE mode for TextureCoordinateGenerator would
> generate texture coordinates based on the local slope angle (
> implementations could derive the slope on the local normal ). By default
> slopes from 0 to 90 degrees would be scaled to the 0 to 1 range of the S
> texture coordinate. The  parameter field could be used to define a custom
> range. T would be set to 0 and a 1d texture map would be expected.
>
> Here are two examples:
>
>
> http://andreasplesch.github.io/x3dom/GeoElevationGrid_texture/puddle_slope.xhtml
>
> and
>
>
> http://andreasplesch.github.io/x3dom/GeoElevationGrid_texture/face_slope.xhtml
>
> using a tentative implementation in a forked x3dom (Mesh.js).
>
> One could also imagine (and quite easily implement) another mode
> "HEIGHT-SLOPE" which uses both attributes as S and T respectively  and a 2d
> texture map as suggested by Simon Thum on the geospatial list.
>
> These modes would be somewhat similar to the existing VERTEX and
> SPHERE-LOCAL modes but aimed at 1d texture maps.
>
>
>
> Finally, geospatially registered meshes would need equivalent modes using
> height above the geoid and slope relative to the local tangential plane to
> the geoid.
>
> Thanks for reading,
>
> -Andreas
>
>
> --
>
> Andreas Plesch
> 39 Barbara Rd.
> Waltham, MA 02453
>



-- 
Andreas Plesch
39 Barbara Rd.
Waltham, MA 02453
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